1. Field of the Invention
The present invention relates to a source address selection system, a router device, a communication node and a source address selection method for selecting an egress node appropriately, in the case where the homes, SOHOs, etc., are constantly connected by the Internet through a plurality of ISPs by using IPv6.
2. Description of the Related Art
In recent years, the utilization of the world largest computer network “Internet” has been spreading, and new computer businesses have been developed by accessing the Internet and utilizing disclosed information or services, or by providing information or services to external users who make accesses through the Internet. Also, new technological developments regarding the Internet utilization have been in progress. On the Internet, each computer has an identifier called IP address, and the packet exchanges are carried out according to this IP address. Usually, in the case of accessing the Internet, the user can have an address allocated by making a contract with an ISP (internet Service Provider).
Currently, the IPv6 address is allocated on the provider base. Namely, a partial set of the addresses already allocated to the provider is allocated to the user when the user makes a contract with that provider.
In future, it is expected that even a small scale network such as that of the home or the SOHO will make contracts with a plurality of providers for the purpose of the stable utilization of the Internet or the like. In such a case, there will be a plurality of access points between this network and the Internet, and this situation is referred to as a multi-home.
As shown in FIG. 12, suppose that a node N is connected to the Internet through providers A and B. In the IPv6, the node can have a plurality of addresses, so that in this case, the Node N can use an address allocated by the provider A and an address allocated by the provider B.
Here, in FIG. 12, suppose that a trouble occurs at the provider A such that it became impossible to deliver packets from the Internet to the node N via the provider A.
Even if the node N tries to carry out communication with a server S by using an address belonging to the provider A as a source address, it is impossible to carry out a communication with the server S. This is because even if a packet is transmitted from the node N by using an address belonging to the provider A as a source address, a route to the server S is disconnected due to the trouble occurring at the provider A side.
This can be resolved if it is possible to change a route such that the packet destined to an address belonging to the provider A can reach via the provider B, as done in the current IPv4 protocol. However, such a change of a route can lead to a considerable expansion of the routing table, and its realization is quite difficult in the IPv6 protocol which has a vast address space by using the prior art.
Now, suppose that the packet with an address belonging to the provider A as a source address reaches to the server S via a route of the provider B. In this case, when the packet having an address belonging to the provider A as a source address is received, the server S tries to establish a communication via a route of the provider A in an attempt to carry out a communication with a source node according to this source address. However, the reply packet from the server S cannot reach the node N because the provider A has a trouble, and a communication cannot be carried out. In addition, in the IPv6, an ingress filter (IETF RFC 2267 and RFC 2827) is employed very often, but when it is employed, the packet having an address belonging to the provider A is not allowed to pass through the provider B in the first place, so that the packet will not reach the server S.
In the SOHO or the like, if the multi-home cannot be utilized efficiently due to such a problem, it is difficult to improve the reliability of the Internet.
As described, in the prior art, it has been difficult to utilize the multi-home effectively under the IPv6 environment.